A manufacturing process of a semiconductor device includes various process steps that perform various heat treatments, such as an oxidation treatment, a diffusion treatment, a CVD treatment, and an annealing treatment, to process objects, e.g., semiconductor wafers. A vertical heat treatment system capable of heat-treating plural wafers at one time has been used as one of heat treatment systems for performing the foregoing process steps.
The vertical heat treatment system includes: a heat treatment furnace; a holder (also referred to as “wafer boat”) that is loaded and unloaded into and from the heat treatment furnace while the holder holds plural wafers at vertical intervals; and a transfer mechanism that transfers wafers between the holder and a container (also referred to as “carrier” or “cassette”) for holding therein plural wafers at predetermined intervals. The transfer mechanism includes: a base capable of vertical movement and rotation; and plural substrate support devices mounted to the base and being capable of anteroposterior movement, and of holding wafers, respectively (See JP2002-164406A, for example).
The transfer mechanism comprises a robot that automatically performs predetermined transfer work in accordance with a control program stored in the controller of the robot. In order to enable such a transfer mechanism to transfer wafers to their appropriate positions within the holder or the container, the operator performs teaching of wafer transfer target points while the operator manually (i.e., non-automatically) operates the transfer mechanism in a remote-control mode.
The teaching accuracy depends on the skill of the operator. Thus, the teaching work is sometimes time-consuming, or teaching of target points with sufficient accuracy is sometimes impossible. In addition, a dummy wafer, which is placed at a predetermined place within the holder, is not transferred in every process but is continuously placed at the predetermined place for a long time. Thus, the dummy wafer is likely to be displaced due to vibration or the like. Under the circumstances, the position of the dummy wafer is regularly corrected so that the dummy wafer is returned to its right position. It is difficult to perform the correction rapidly and accurately by means of a conventional transfer mechanism. If a wafer is not held at an appropriate position within the holder, for example, if the wafer sticks out of the holder, an accident such as fall or damage of the wafer may possibly occur.